The invention relates to a rotary valve that comprises several means that allow the circulation of fluids, whereby the means are arranged to produce the simultaneous linking of different hoses according to a predetermined sequence.
A valve according to the invention is used in particular to link several hoses that can be classified in several groups, defined, for example, according to their function. The connection between the different groups is made, for example, according to a predetermined sequence.
The invention is used, for example, in a process for separation that uses four process fluids such as feedstock, extract, raffinate and desorbent. The different groups can be specified in the following manner:
GROUP 1, G1=the hoses that allow the transfer of fluids from said process fluids, such as extract, raffinate, feedstock and desorbent;
GROUP 2, G2=the hoses that allow the linking to be carried out between the different openings that are arranged at the rotary valve;
GROUP 3, G3=the hoses that allow a process fluid to communicate with a bed of a separation column or between two beds (bypass fluid).
The concept of group that is provided relative to hoses can be extended within the scope of this application to the fluids in question.
By using a single device, the prior art describes the possibility of linking, on the one hand, four external flows (solvent, extract, feedstock, raffinate) and two rinsing flows (inlet and outlet), and, on the other hand, producing 24 connections to 24 adsorbent beds.
For example, U.S. Pat. No. 3,040,777 and U.S. Pat. No. 3,422,848 describe rotary valves that comprise a rotor and a stator.
In U.S. Pat. No. 3,040,777, the rotor comprises on its lower face several grooves for the circulation of process fluids, whereby each groove communicates with a line for admission or evacuation of these fluids. Several openings that are distributed along a circle pass through the stator according to its thickness. These openings communicate with the 24 lines that allow the connection with 24 beds of a separation column. Channels for the passage of two rinsing flows are arranged in the central zone of the stator. A liner that is arranged on the upper face of the stator ensures the sealing between the grooves, between the grooves and the 24 orifices of the 24 beds and also between the 24 orifices. An upper dome in airtight connection with the stator forms a chamber. A fluid that is introduced by a hose in connection with the dome puts the chamber under pressure.
U.S. Pat. No. 3,422,848 relates to an improved liner for withstanding problems of erosion and mechanical deterioration that is produced by the stator-rotor contact, when these two elements are rotating. In this document, the grooves are arranged on the upper face of the stator in a manner that is concentric to the center or axis of rotation of the valve. The communication between the grooves and the orifices for circulation of fluids is ensured by xe2x80x9cUxe2x80x9d-shaped or jumpover hoses.
In practice, these two types of valves that are widely used have good operating reliability. They are limited, however, in their applications. For example, used in separation processes in a simulated moving bed, they do not make it possible to carry out a continuous rinsing of all of the distribution tentacles and of all of the lines that connect the beds to the rotary valve is not feasible. Inlet and outlet rinsing lines are provided to balance in part this drawback.
The prior art also describes two adaptations of the above-mentioned valves for specific communications of the inlet and the outlet of each of the beds with the four or six inlet or outlet flows.
U.S. Pat. No. 4,614,204 maintains the principle of concentric grooves, while U.S. Pat. No. 4,633,904 describes the use of a number of openings that are used at the stator instead of grooves.
These two latter teachings relate to a rotary valve for the connection of a series of independent columns that each contain an adsorbent bed, with the following particular feature: the end of each of these columns may or may not be connected to the next. The stator comprises two series of orifices that are arranged along two concentric crowns. A first series of orifices is connected to the inlet of each of the columns, and a second series of orifices is connected to the outputs of the columns.
The function of these orifices is to ensure the passage of fluids between the separation columns. Because of the similarity of the circulating fluids, the orifices of the first series have, for example, identical characteristics to the orifices of the second series. The number of hoses for linking, two by two, three groups of openings of the stator (column inlet, column outlet and communication to an outside fluid) is naturally much larger than the six flows that are provided in U.S. Pat. No. 3,422,848. For 24 beds and six outside flows, there are thus 30 linking hoses that have to stand in the small space constituted by the upper stator.
Finally, the prior art can be illustrated by U.S. Pat. No. 4,923,616 and U.S. Pat. No. 4,705,627.
The object of this invention is a rotary valve that makes it possible to link different groups of hoses as defined above.
The rotary valve according to the invention pertains particularly well to a chromatographic separation column of at least one aromatic isomer with 8 carbon atoms in a simulated moving bed in a mixture of xylenes and ethylbenzene by containing, and preferably paraxylene, with a view to the terephthalic acid synthesis, an intermediate petrochemical product in the production of textiles.
More generally, it can be used in a process for separation of at least one isomer in a mixture of components that is difficult or impossible to separate by distillation or by crystallization.
It can also be applied in a process for separation of at least one component in a mixture where an adsorption or ion-exchange chromatographic separation is used, for example.
It pertains in particular to improving the process and the device that are described in Patent Application FR 97/16,273. In short, this application teaches in particular taking a portion of the main fluid to reinject it into the circulation space of a sector where the pressure is lower via the orifices of the distribution chambers in question.
When the distribution chambers are connected with the outside of the column by a single distribution basket, and when it is desired to establish circulation between two consecutive adsorbent beds, the diagram of individual valves and bypass lines that is provided in the above-mentioned patent application would lead to a parasitic circulation parallel to the separation column.
When each of the distribution plates is equipped with at least two independent fluid distribution networks (D1 and D2), for example, network D1 of plate P is linked with network D2 of plate P+1, and network D2 of plate P+1 is linked with network D1 of plate P+2. In this way, for each of the distributor plates, all of the distribution networks permanently channel a circulation of fluid, and each of the plates experiences a first flow of bypass fluid from a distribution network to the main fluid and a second flow of bypass fluid that is approximately equal from the main fluid to the second distribution network. The driving force of these flows is ensured by the pressure drop that is caused by the flow of main fluid into the porous granular medium that is located between two successive distributor plates.
When each of the distributor plates is equipped with only a single distribution network, the bypass lines can establish only one bed out of two, for example, from plate P to plate P+1, then from plate P+2 to plate P+3. Actually, if a bypass line connected plates P+1 and P+2, a circulation that is parallel to the adsorbent beds from the top bed to the bottom bed would result. To establish the bypass only in one bed out of two would involve a variation of the internal flows from one bed to the next. In the beds that comprise a bypass, a flow rate D would result while on the beds that do not comprise a bypass, a flow rate of D+d would result.
This invention relates to a rotary valve that makes it possible to link several groups of hoses referenced group G1, group G2 and group G3, whereby said valve comprises at least:
a stator that is provided with means (E, F, R, S) for circulating fluid or fluids of group G1, means for passing at least two fluids F1, F2 that belong to group G31,
a rotor that is equipped with means for passing fluids of group G3 and also means that make possible the linking either of fluids of group G1 with group G3 or fluids of group G3 with group G3.
The valve is characterized in that the number of means for passing for fluid F1 is approximately identical to the number of means for passing for fluid F2, said valve comprises means for linking at least two fluids of group G3 and in that passage section S1 for openings intended for fluid F1 is different from passage section S2 for openings intended for fluid F2.
According to an embodiment, the means for passing for fluid F1 and for fluid F2 have passage surface areas, respectively S1 and S2, and in that the S1/S2 ratio is approximately equal to 4, and preferably between 2 and 10.
The means for linking fluids of group G3 consist of, for example, slots that are arranged in a layer of material or liner that is deposited on the lower face of the rotor.
A slot has, for example, a depth xe2x80x9cpe,xe2x80x9d and the value of the depth is at least equal to thickness xe2x80x9cexe2x80x9d of the liner.
Circulation means (E, R, S, F) can be formed by several grooves that are arranged on the support face of the stator, and the slots are arranged in, for example, the liner.
The number of circulation means (E, R, S, F) is, for example, equal to 4.
The invention also relates to a system for chromatographic separation of a feedstock in a simulated moving bed separation device that comprises a number of beds (A1 to An) of a solid or an adsorbent that are contained in a column, whereby two adsorbent beds are separated by at least one fluid distributor plate (Pi) between each bed, a distributor plate (Pi) comprises at least one distribution chamber (Ci) that is provided with orifices and a space for circulation of a fluid near said orifices of the chamber, said chamber being connected to a transfer line (Li) that extends between the chamber and a point that is located outside of the column, and whereby line (Bi) makes it possible to inject a bypass fluid, means for circulation of the fluid outside of said separation device. The system is characterized in that transfer lines Li, bypass lines Bi and transfer lines of process fluids are connected with at least one rotary valve V that has one of the characteristics that are mentioned above for the rotary valve according to the invention.
The system comprises, for example, a bypass line Le of at least a portion of the fluid before its introduction into the first stage of said separation column, whereby said line Le is connected to the pumparound line and rotary valve V.
According to an embodiment, the system comprises at least one bypass line Le that is connected between rotary valve V and the pumparound line upstream from the recirculation pump.
The separation column comprises, for example, 24 adsorbent beds.
According to an embodiment, the separation column comprises 24 adsorbent beds that are distributed in two separate chambers and connected via hoses and means for circulation of the fluid.
The invention also relates to a process for separation of a feedstock by chromatography.
The process is characterized in that it comprises at least the following stages:
said feedstock that is to be separated is injected into a separation column that comprises a number of beds (A1 to An) of a solid or an adsorbent that are contained in a chromatographic column, whereby two adsorbent beds are separated by at least one fluid distributor plate (Pi) between each bed, a distributor plate (Pi) comprises at least one distribution chamber (Ci) that is provided with orifices, and a space for circulation of a fluid near said orifices of the chamber, and whereby said chamber is connected to a transfer line (Li) that extends between the chamber and a point that is located outside of the column, and a line (Bi) makes it possible to inject a bypass fluid, means for circulation of the fluid outside of said separation device,
various fluids are injected or extracted: at least the process fluids, the bypass fluid and the main fluid in various beds Ai, according to a predetermined sequence and via a rotary valve V that has the above-mentioned characteristics for the rotary valve according to this invention, whereby said transfer lines Li, bypass lines Bi and process fluid transfer lines are connected with said rotary valve.
According to an implementation, at least a portion of the main fluid is derived before its injection at the top of the separation column to send it directly to rotary valve V.
For example at the last stage of the separation device, the bypass fluid is sent directly from rotary valve V to the pumparound line upstream from the recirculation pump.
The rotary valve according to the invention, or the separation system that comprises the above-mentioned characteristics or the separation process are used, for example, to separate at least one aromatic isomer with eight carbon atoms in a mixture of xylenes and ethylbenzene.